There is a voice recognition technology in which a plurality of pieces of information ranked by an index such as likelihood or the like are identified as results of recognition of received voices. In such a voice recognition technology, when the volume of input voice is too low, accuracy of voice recognition is lowered due to the effect of environmental sound. The accuracy of voice recognition is lowered also when the volume of input voice is too high. Then, when the accuracy of voice recognition is low, information that a user desires to make recognized is identified as a result of recognition having a low recognition ranking, or is not identified as a result of recognition. Therefore, in order for information desired to be recognized to be identified as a result of recognition having a high recognition ranking, the user needs to input voice at a volume at which to perform the input.